This invention relates to a method for machining a clutch gear for the transmission of an automobile, and particularly, relates to a method for machining a clutch gear for the transmission of an automobile comprising a first step of providing a rough shape of a generally round annular bar made of a malleable material. The round bar may be made in a cold forging or a hot forging. The process also includes a second step of urging the generally round bar against a die and simultaneously forming a final predetermined dimensional cross section and a chamfer projection, a third step of blanking the chamfer projection into a tooth form by a fine blanking process, and a fourth step of pushing said form into a die from an end surface opposite the chamfer projection and forming an inverted taper on the tooth form which prevents disengagement of the clutch.
Heretofore, as a machining process for clutch gears, prior art such as the invention of Japanese patent publication No. 47-14696 existed for cold plastic machining. The invention disclosed in the Japanese official gazette comprises a first step of forming an annular portion of an almost rectangular cross section and of at least a predetermined dimension on an annular member or a disc member made of a malleable material, a second step of abutting a die having a plurality of radial grooves of a triangular cross section against an end surface in the axial direction of the annular portion to form a chamfer projection, a third process of abutting the die having a plurality of teeth on the end surface of the annular portion to be worked so that the teeth end portions thereof are positioned between the adjacent chamfer projections and applying pressure in the axial direction to form continuous teeth on the chamfer projection and a push wall on the ends of these grooves, a fourth step of blanking and removing the push wall portion which is not continuous with the teeth, and a fifth step of pushing the annular portion into a die having teeth consisting of a tapered side wall and a tapered bottom from the end surface opposite the chamfer projection and forming an inverted taper on the teeth of the annular portion to prevent disengagement of the clutch. However, the technique of the invention of the prior application has the following problems. Namely, in the first place, many machinings are required, and in the second place, when the push wall is blanked in the tooth portion, there is a problem in the blanking precision of the tooth top and the bottom land. Also, there is a need to machine the tooth top and the end surface of the tooth opposite the chamfer since burrs are produced on the end surface of the tooth and the side opposite the chamfer side. In the third place, referring to FIG. 1, FIG. 1 is a drawing showing the relationship of the gear clutch (1) and the sleeve (2) in a synchro-mechanism, and FIG. 1A is the structure in which the peripheral surface is machined by leaving the tooth top opposite the chamfer (1a) of the tooth form portion to produce a stop member (1b) for prevention of overshift in the direction of arrow mark of the sleeve, and in the conventional machining process, this structure is known. FIG. 1B is the structure in which a stop member (1d) for overshift is provided at the tooth top of the spline in the sleeve so that overshift is prevented upon abutment with the end surface of the chamfer side (1 e) of the gear clutch (1). Accordingly, in case of the example of FIG. 1B, high precision is required over an entire width of the tooth portion since the tooth top and the bottom land of the gear clutch (1) fit completely with the sleeve (2). Also, a surface (1f) continuous with the chamber ridge which acts as a stopper at the gear clutch side is needed, and the role of the stopper is not served if the concave portion (1c) exists at the chamfer side of the bottom land of the gear clutch shown in FIG. 1A. Accordingly, in the gear clutch to be used in the example of FIG. 1B, there is a drawback that cannot be dealt with by the conventional processing method.
As described in the foregoing, in the conventional machining process or in the technique of the invention disclosed in the Japanese patent publication No. 47-14696, there are many problems and drawbacks.